Free piston pump

ABSTRACT

The invention is a free-piston pump incorporating an integral switching valve modified for fail proof operation.

United States Patent [191 Robbins, Jr.

FREE PISTON PUMP Inventor: Roland W. Robbins, Jr., Ridgecrest,

Calif,

The United States of America as represented by the Secretary of the Navy, Washington, DC.

Filed: Nov. 26, 1973 Appl. No.: 419,013

Related U.S. Application Data ('ontinuution-in-pnrt of Ser. No. 250,302, May 2, I972, abandoned.

Assignec:

U.S. Cl 417/393, 91/329,, 91/338 Int. Cl. F04b 17/00 Field of Search 417/393, 383,395, 404; 91/329, 337. 338

[ 1 Nov. 5, 1974 [56] References Cited UNITED STATES PATENTS 3,276,381 l0/l966 Harklau et ul 9l/329 X 3,329,094 7/1967 Harklnu et al. 4l7/393 Primary Eraminerwillinm L. Frcch Assistant Examiner-Richard Sher Attorney, Agent. or FirmR. S. Sciuscia; Q. E. Hodges [57] ABSTRACT The invention is a free-piston pump incorporating an integral switching valve modified for fail proof operation.

1 Claim, 3 Drawing Figures J xtnnnmw 60E? WAY fl e g knaok stv 1 FREE PrsToN PUMP This application is a continuation-in-part of application Ser. No. 250,302 filed May 2, 1972 and now abandoned.

BACKGROUND OF THE INVENTION In the past, several free-piston pumps have been available on the market. Typical of the prior art of the pumps disclosed in US. Pat. No. 657,160 issued to Eads on Sept. 4, 1900 and US. Pat. No. 3,276,381 issued to Harklau et al. on Oct. 4, 1966. The double acting free-piston pumps of the prior art which use one or more concentric shuttle valves are unreliable in high pressure applications particularly where the fluid being pumped is contaminated with small solid particles such as sand. The spring force was often unable to move the shuttle since sand and dirt particles would lodge between the sliding surfaces. Therefore, the reliability of prior art pumps is limited. Only when the fluid in contact with the piston is a relatively uncontaminated fluid such as oil are they reliable. Indeed, one of the motives for the use of the diaphragm system of the Harklau et al. device is to prevent contact between a contaminated fluid and the piston mechanism.

SUMMARY OF THE INVENTION The invention is a double acting free-piston pump which incorporates shuttle valving features which in- OBJECTS OF THE INVENTION It is a primary object of the instant invention to provide a simple reliable pump that can be used to pump seawater in a buoyancy control system of a small deep diving submersible.

It is another object of this invention to provide a shuttle valve mechanism in a free-piston pump which insures reliable operation on particle contaminated fluids.

It is another object of this invntion to provide a reliable pump for any liquid or gaseous media which may be contaminated with solid particles.

Other objects, advantages and novel features of the invention will become apparent from the following detailed description of the invention.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a partial cross-section of the pump of this invention;

FIG. 2 is a detailed cross-section of the shuttle, porting block and right piston arrangement; and

FIG. 3 is a detailed cross-section of'the left piston and end cap arrangement.

DESCRIPTION OF THE PREFERRED EMBODIMENT With continued reference to the drawings, the body of the pump consists of a cylindrical tube 1 opened at both ends. Within this cylinder and positioned midway between the ends is a porting block 3. Centrally located and axially aligned with the porting block is a shuttle valve 5 which is free to reciprocate within the porting block between limits. Centrally located and axially aligned with the shuttle valve 5 is a piston rod 7. The piston rod is free to reciprocate within the shuttle valve. Attached to the ends of the piston rod 7 are pistons 9 and 2. The pistons and piston rod assembly are free to reciprocate as a unit.

Each valve block 15 contains a set of check valves 17. One check valve allows flow into the pump and blocks flow in the reverse direction while the other valve performs the opposite function, thus insuring unidirectional flow through the pump during operation.

The free-piston pump operates when hydraulic power is supplied to the free-piston pump through port 19. Port 19 is the inlet and port 21 is the discharge. High pressure hydraulic fluid is directed into inlet 19 to central bore 40. Sliding spool 5 freely moves transversely within central bore 40. Sliding spool 5 has annular indentations which direct the high pressure fluid to either chamber 37 or 55 depending upon its position within the porting block. The position and motion of the sliding spool is controlled by the motion of pistons 9 and 2. Pistons 9 and 2 are rigidly interconnected by rod 7 which passes through sliding spool 5.

In the drawings the pistons are shown moving toward the left. Piston 2 is just contacting sliding collar 60. This contact is the first in a series of events which will aggregate to insure the reciprocating of sliding spool 5 to the left most position and cause the driving fluid to force the pistons to the right. A symmetrical operation will then be initiated to send the piston arrangement again to the left.

After piston 2 contacts the sliding collar and moves it to the left the detent balls 27 will be free to move outwardly and release the spool from the locked position.

I The detent balls lock the spool into position by engaging an annular groove in the spool. Prior to contacting the sliding collar the leftward motion of the piston caused spring 45 to be compressed between piston 2 and sliding spool 5. Therefore, when the detent balls are freed by the movement of the collar the spool is free to be forced by spring 45 to its leftmost position. If the sliding spool moves to the left it will do so until retaining ring 62 engages porting block 3. When the leftmost position is reached the left annular groove in the sliding spool will be positioned directly under the left set of detent balls 28. The detent balls will move radially inward and engage the annular groove. Sliding collar 61 will move leftward as forced by spring 29. The spool will now be locked in its leftmost position.

If the spool binds and does not move under the force of spring 45 a further series of mechanical events will take place to insure the movement of the spool. If, for example, the spool does not move because of an excessive build up of pressure in left chamber 37 between the left piston 9 and the central valve mechanism. This pressurewould act against the left face of sliding spool 5 urging it to remain in its rightmost position against spring 45. This excessive pressure will cause piston 9, and thus the entire pistonassembly, to continue leftward and the connecting rod 7 will therefore move to extend slots 12 into chamber 37. The slots 12 in the surface of rod 7 extend to a reduced diameter section 14 of the rod. Thus, the high pressure fluid in chamber 37 is allowed to flow through slots 12 to the reduced diameter section 14 and into exit channel 35 to exit port 21. The excessive pressure having been released, the shuttle now moves leftward under the action of spring 45.

If, after the bleading of the high pressure fluid from chamber 37, the spool remains in its rightmost position a final event will occur to insure the movement of spool 5. This failure of the spool to move may be caused by a particle jamming the spool in its position. When the spool remains in position, even after the above described bleading, surface 55 of piston 2 will engage the end face of spool and force it into its leftmost positron.

' FIG. 3 is a cross-section of the left side of the pump of the instant invention. The FIG. indicates the relative piston assembly displacement for each of the events in the series of events designed to insure reciprocal movement.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore, to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

l. A fail safe free piston pump, comprising:

a cylindrical housing with a first and second end;

an inlet and an exhaust check valve at each of said first and second ends to admit and expel] the fluid to bepumped into and out of the housing;

valve means located within said housing between said ends of said cylinder forming a first and second chamber within said housing, said valve comprising an axially slidable shuttle valve which directs a pressurized driving fluid from an external source alternatively to said first and second chamber as said shuttle valve reciprocates axially;

first and second pistons slidably mounted within said housing on opposite sides of said valve means said pistons being driven by pressurized fluid;

a rod means interconnecting said pistons and slidably and concentrically mounted within said shuttle valve;

shuttle valve engaging and release means associated with each piston to releasibly hold said shuttle valve in a first and second position comprising a pair of retaining balls, a concave detent on the surface of said shuttle valve to receive said balls, a sliding collar means to selectively fix said balls within said detent to hold the shuttle valve in a fixed position;

a spring attached to each of said pistons to bias the shuttle valve during a portion of the stroke of the 7 said detent balls. 

1. A fail safe free piston pump, comprising: a cylindrical housing with a first and second end; an inlet and an exhaust check valve at each of said first and second ends to admit and expell the fluid to be pumped into and out of the housing; valve means located within said housing between said ends of said cylinder forming a first and second chamber within said housing, said valve comprising an axially slidable shuttle valve which directs a pressurized driving fluid from an external source alternatively to said first and second chamber as said shuttle valve reciprocates axially; first and second pistons slidably mounted within said housing on opposite sides of said valve means said pistons being driven by pressurized fluid; a rod means interconnecting said pistons and slidably and concentrically mounted within said shuttle valve; shuttle valve engaging and release means associated with each piston to releasibly hold said shuttle valve in a first and second position comprising a pair of retaining balls, a concave detent on the surface of said shuttle valve to receive said balls, a sliding collar means to selectively fix said balls within said detent to hold the shuttle valve in a fixed position; a spring attached to each of said pistons to bias the shuttle valve during a portion of the stroke of the piston; and a ring integral with each of said pistons which engages said sliding collar to move it axially and free said detent balls. 